prasadrmb

It is not advisable to have in two different levels. You have to consider the stress distribution here. Foundation at the lower level does not have much problems but the foundation at top is critical. If the somebody excavated around the foundation area that is affect to the bearing capacity of the foundation. For example consider, even after construction, some body excavating the gap between the foundations. Bearing capacity assumed for the foundation at top will be reduced and it can cause additional settlements http://structuraldesignbs.blogspot.com/

Since you have not given much information's, In general, it is not advisable to consider beams supports as fixed supports. If the beam is connected with very rigid column you may consider support condition as fixed. But other cases you may not take as fixed. Generally, the end span moment is comparatively higher than the other spans. When you consider the boundary condition fix, then span moment will reduce. You are designing for a smaller moment. If the assumed fixity is not generated after construction (depends on the end column stiffness) span moment will be higher and reinforcement provided will not be adequate. This can lead to failure. http://structuraldesignbs.blogspot.com/